This invention, as noted, relates to magnetic disk drives, specifically those of the type in which position information is encoded onto portions of the disk. The disk is divided into sectors for the recording of data. At the time of manufacture of the disk the sectors are defined by index marks which are encoded radially across the surface of the disk, without regard to specific track. The tracks are defined by writing of additional signals at the beginning of each track, following the index mark. The data field follows the position information in each track per each sector. This is in distinction to a prior art practice in which position data was written to a complete track; that is, at least one track contained no data field.
It will be appreciated by those skilled in the art that it is important to control the position of the read/write head with respect to the track, both as to proper maintenance of the disk over the center of the track when a desired track has been located, and in connection with moving the head from one track to another upon command; that is, during a "seek" operation. According to co-pending application Ser. No. 257,608 filed Apr. 27, 1981, position data written immediately following the index mark is used in a servo loop to maintain centering of the head over the track. Clearly, it would be advantageous to use as much of this circuitry as possible in the control of a seek operation. Moreover, it would be desirable to accomplish the seek operation in an expeditious and as rapid a fashion as possible, and moreover, to do so without additional circuit complexity. Those skilled in the art will recognize that one possible way of implementing a seek operation is to calculate in advance each of the acceleration, steady-speed and deceleration operations performed by the head with respect to the disk during a seek operation, but will additionally recognize that to store each the individual acceleration, constant-velocity and deceleration segments of each seek profile would require large amounts of memory. Accordingly, it would be desirable to avoid this practice.